South Africa's anti-graft watchdog will investigate the government's providing of protection services to former African Union (AU) Commission chair Nkosazana Dlamini-Zuma, its spokesman said on Sunday.

Dlamini-Zuma, once married to President Jacob Zuma and seen as a front-runner to succeed him, in March concluded her five-year tenure as AU Commission chairwoman and has made several public appearances in South Africa since.

An investigation into Dlamini-Zuma, seen as Zuma's preferred candidate by political analysts, is bad news for the scandal-plagued president who survived a no-confidence vote by his own party's highest body last week.

The Democratic Alliance (DA), the largest opposition party, in April complained that Dlamini-Zuma is enjoying protection services afforded to visiting heads of state or elected representatives, while she holds no official position.

"Dlamini-Zuma is a clear candidate in the ANC leadership succession race, and her use of VIP Presidential Protection as she campaigns is clearly another ANC abuse of public money," the Democratic Alliance said in a statement on Sunday.

The Public Protector's spokeswoman, Cleopatra Mosana, said the anti-graft watchdog will investigate Dlamini-Zuma's use of VIP protection services.

"Yes it will," she said, without elaborating.

The African National Congress' women's league endorsed the party veteran and former minister as presidential candidate in January, though the ruling party has not officially given the go-ahead to campaign for an elective conference in December.